Abstract

On activation, naive T cells differentiate into effector T-cell subsets with specific cytokine phenotypes and specialized effector functions. Recently a subset of T cells, distinct from T helper (T(H))1 and T(H)2 cells, producing interleukin (IL)-17 (T(H)17) was defined and seems to have a crucial role in mediating autoimmunity and inducing tissue inflammation. We and others have shown that transforming growth factor (TGF)-beta and IL-6 together induce the differentiation of T(H)17 cells, in which IL-6 has a pivotal function in dictating whether T cells differentiate into Foxp3+ regulatory T cells (T(reg) cells) or T(H)17 cells. Whereas TGF-beta induces Foxp3 and generates T(reg) cells, IL-6 inhibits the generation of T(reg) cells and induces the production of IL-17, suggesting a reciprocal developmental pathway for T(H)17 and T(reg) cells. Here we show that IL-6-deficient (Il6-/-) mice do not develop a T(H)17 response and their peripheral repertoire is dominated by Foxp3+ T(reg) cells. However, deletion of T(reg) cells leads to the reappearance of T(H)17 cells in Il6-/- mice, suggesting an additional pathway by which T(H)17 cells might be generated in vivo. We show that an IL-2 cytokine family member, IL-21, cooperates with TGF-beta to induce T(H)17 cells in naive Il6-/- T cells and that IL-21-receptor-deficient T cells are defective in generating a T(H)17 response.

Depletion of Treg cells in Il6−/− mice restores the development of TH17 cells and susceptibility to EAE

Il6−/− × Foxp3gfp.KI mice were treated with antibody against CD25 to deplete Treg cells or with a control immunoglobulin (rat IgG1) and then immunized with MOG35–55/CFA. a, b, Clinical EAE scores (means and s.e.m.) (a) and linear regression analysis in acute (b, top) and chronic (b, bottom) stages of the disease for wild-type (WT), control Il6−/− and Treg-depleted Il6−/− mice (n.s., not significant). c, Lymph-node (LN) cells and mononuclear cells from the central nervous system (CNS) were recovered on days 6, 14–17 (peak disease) and 29 (recovery) and stained for CD4 and intracellular IL-17 and IFN-γ. The numbers in the quadrants show percentages. d, Splenocytes (day 10) were stimulated with MOG35–55in vitro. Culture supernatants were collected after 48 h, and IL-17 and IFN-γ concentrations were determined. Filled circles, WT (IgG); open triangles, Il6−/− (IgG); open circles, Il6−/− (anti-CD25).

Inhibition of induction of Treg cells and generation of TH17 cells by IL-21

CD4+CD62LhiFoxp3/GFP− T cells from Foxp3gfp.KI mice were stimulated with anti-CD3 and anti-CD28 for three days in the presence of the indicated cytokines. a, The expression of Foxp3/GFP was measured and the fraction of Foxp3+ cells induced by TGF-β was normalized to 100%. b, Individual histograms showing Foxp3/GFP expression. The numbers above the histogram regions (horizontal lines) represent the percentages of Foxp3/GFP+ cells. c, IL-17 production in these cultures after 48 h as measured by ELISA. d, ROR-γt expression as determined by quantitative RT–PCR in naive 2D2 () T cells activated for 48 h with anti-CD3 in the presence of irradiated syngeneic antigen-presenting cells and the indicated cytokines. ROR-γt expression is shown as mean and s.e.m. for duplicate determinations, relative to β-actin.